1. Field of the Invention
The invention relates to a method for supporting low-level flights in which an obstacle warning is provided for the pilot, whereby information on the topography of the surrounding terrain is collected by at least one sensor located on the aircraft, whereby the information represents raw data, and whereby an image-like representation is calculated from the overall raw data.
2. Description of Background and Relevant Information
Overhead lines and wires can constitute a significant hazard to low-flying aircraft such as helicopters, for example, due to the operational spectrum of applications, i.e., the wide range of applications in which such aircraft are called-upon to operate. In contrast with relatively large solid obstacles, such as, e.g., mountainsides or valley walls, large buildings, edges of forests, or dense groups of trees, there are other obstacles, particularly overhead lines, i.e., cables and wires, e.g., which characterized by their very low visual contrast to their surroundings. This can mean that pilots of such aircraft risk not recognizing such line obstacles until very late, giving rise to critical flight situations.
Sensors based upon laser scanning or imaging radar technology can provide obstacle information in the form of distance images, i.e., image matrices of distance measurement pixels. The problem lies in the development of a method for recognizing lines or line pixels in these distance images that can be performed in real time so that the pilot can be adequately warned about such objects in a targeted manner.
Methods for recognizing lines, such as cables or wires, by means of the Hough transform are known from DE 100 55 572 C2 and U.S. Pat. No. 6,747,576 B2. These methods are aimed at recognizing the line as an entire object and are correspondingly complex and time-intensive in terms of computing. The capacity of conventional processors is too small to carry out the calculations of these methods in real time.
Other methods recognize line pixels solely by searching for sudden changes in the distance value of a pixel compared with those adjacent to it within the column in the distance image. A method of this type is known from DE 198 28 318 C2 and UK Patent Application Publication No. 2 341 506 A. Since it must also be possible to recognize lines when seen against the sky—where there are no valid distance measurement values—a pixel must also be classified as a line pixel when it is surrounded in the column by adjacent pixels with invalid distance values. However, invalid measurement pixels do not occur only when the sensor faces towards the sky, they also occur sporadically, through solar radiation and particularly often through reflections on smooth surfaces, such as, e.g., bodies of water, asphalt streets and squares, take-off or landing runways or helicopter landing airfields. With the method according to DE 198 28 318 C2 these invalid measurement pixels lead to incorrect interpretations of measurement pixels as line pixels, the accumulation of which in particular in the area of take-off and landing runways or with bodies of water considerably restricts the reliability of this method. This has negative effects on the operational applicability in an obstacle warning system for low-flying aircraft.